1. Field of the Invention
The present invention relates to a heat sink for cooling an integrated circuit element such as a central processing unit (CPU), a video chip, and so forth, incorporated into an electronic apparatus such as a computer, and so forth. The present invention also relates to a method of attaching the heat sink and an electronic apparatus in which the heat sink is incorporated.
2. Description of the Prior Art
As the electric power consumption of a CPU, which is incorporated in an electronic apparatus such as a computer, is great, the CPU is conventionally cooled with a heat sink or a heat sink combined with a cooling fan.
Recently, it has been tried, on one hand, to decrease the electric power consumption of the CPU, by miniaturization of the CPU in the manufacturing process and on the other hand, the electric power consumption of the CPU has increased due to the increase in the degree of integration of the CPU and valve of the driving frequency of the CPU. That is, there are two contrary factors, so there is a demand for a cooling means, for cooling the circuit elements, the cooling capacity of which is greater than that of the conventional cooling means. Accordingly, although the size of a core and a package of the CPU can be reduced by miniaturization in the manufacturing process even if the degree of integration is increased, a quantity of generated heat is still great. Therefore, it is impossible to use a heat sink, the size of which is smaller than the size of the conventional heat sink.
Accordingly, the size of the heat sink is necessarily larger than the size of the package such as the CPU. With such a heat sink, a conventional fixing means of the type in which the heat sink is fixed by engaging metallic springs with pawls arranged around a socket is used, but it is difficult to fix the heat sink by this fixing means and it is impossible to fix the heat sink in a stable state. Therefore, a cooling means having a retention module has recently been adopted for fixing the heat sink at a predetermined position on a base board such as a mother board. FIG. 5 is a view showing an example of the cooling means having the retention module.
Referring to FIG. 5, detailed explanations will be made with respect to a cooling means having a conventional retention module for cooling a central processing unit (CPU). In FIG. 5, reference numeral 1 is a base board, reference numeral 2 is a CPU socket, reference numeral 3 is a CPU, reference numeral 4 is a heat sink, reference numeral 5 is a clip made of metal, reference numeral 6 is a retention module, reference numeral 7 is a rivet, and reference numeral 9 is a pin.
The retention module 6 is composed as follows. The retention module 6 is formed in a box shape with an open top side, an opening 10 at the center of the bottom portion, the size of which is larger than an external form of the CPU socket 2, and a circumferential wall 12 into which a bottom portion 14 of the heat sink 4 can be received. In this example shown here, the retention module 6 has an engaging section 16 with an inwardly protruding portion so that the engaging section 16 can receive the bottom section 14 of the heat sink 4 when the engaging section 16 is deformed outward. Further, at the bottom section of the retention module 6, there are provided a plurality of holes 18 by which the retention module 6 can be attached to the base board 1. In this case, it is preferable that four holes 18 are formed.
The heat sink 4 is attached to the base board 1 with this retention module 6 by the following method. First of all, the CPU 3 is attached to the CPU socket 2. Then, the CPU socket 2 and the CPU 3 are protruded from the opening 10 of the bottom section of the retention module 6. The retention module 6 is put on the base board 1 so that a plurality of holes 18 of the retention module 6 can align with a plurality of corresponding holes 20 formed in the base board. Rivets 7 having longitudinal through-holes 22 in are inserted into the holes 18 of the retention module and the openings 20 of the base board 1, so that the retention module 6 is temporarily attached to the base board 1. After that, pins 9, the outer diameters of which are a little larger than the inner diameters of the through-holes 22, are press-fitted into the longitudinal through-holes 22 of the rivets 7. Due to the foregoing, the outer diameter of each rivet 7 is expanded by press-fitting, so that the retention module 6 can be locked and fixed onto the base board 1.
After that, when the heat sink 4 is inserted into the retention module 6 while the bottom section 14 of the heat sink 4 is being kept downward, the engaging sections 16 of the retention module 6 are expanded outward. When the upper surface of the bottom section 14 of the heat sink 4 comes to a position lower than the lower end of the engaging sections 16, the engaging sections 16 return to the initial position, and the upper surface of the bottom section 14 of the heat sink 4 can be engaged so that the heat sink 4 cannot come out. Next, a pair of clips 5 made of metal, as shown in the drawing, both end portions of which are bent into an L-shape are engaged with engaging sections (not shown) of the retention module 6 in such a manner that the L-shaped portions of the clips are engaged with the engaging section. (In FIG. 5, only one clip 5 made of metal is shown in the drawing, and the L-shaped portions at both end portions of the clip are not shown in the drawing.) Therefore, the heat sink 4 is given a pressing force, the direction of which is downward, generated by an elastic force of the clip. Accordingly, the bottom surface 24 of the heat sink 4 is made to come into contact with the upper portion of the CPU 3. In this way, heat conduction between the heat sink 4 and the CPU 3 can be improved.
In the cooling means in which the above retention module 6 is used, the circumference of the heat sink 4 is fixed to the retention module 6, and the retention module 6 is fixed onto the base board 1, and therefore, the heat sink 4 can be immovablly and stably attached onto the base board 1. In this connection, although not shown in the drawing, when necessary, a well known cooling fan is arranged at an upper end portion of the heat sink 4 so as to improve the cooling efficiency of the heat sink 4.
However, in the above fixing structure of the conventional retention module 6 and the heat sink 4, the following problems may be encountered. After the plurality of pins 9 have been separately press-fitted into the longitudinal through-holes 22 of the rivets 7, the heat sink 4 is attached to the retention module 6. Therefore, a process in which the retention module 6 is attached and a process in which the heat sink 4 is attached must be separately provided, which causes an increase in the amount of work. In addition to that, as the heat sink 4 is fixed to the retention module 6 only by the pair of clips 5, a pressing force of the heat sink 4 to the CPU 3 is so weak that the attaching strength of the heat sink 4 is low, which deteriorates the reliability of preventing the heat sink from coming out. Further, it is impossible for the heat sink 4 to be uniformly pressed to the CPU 3.
The present inventors made various experiments to solve the above problems. As a result, they found the following. When the heat sink is made to have a function of the above pins, it is possible to solve the problems of the prior art in which a large amount of work is required and the attaching strength is low so that the reliability is deteriorated and it is impossible to push the heat sink uniformly.